1. Field of the Invention
The present invention relates to a data communication system, a data communication method and a data communication apparatus, and, more particularly, it relates to a network in which communication is effected at a high speed while mixing information data (including image data) and command data, and a communication protocol applicable to such a network.
2. Related Background Art
In the past, among peripheral equipments for a personal computer (referred to as “PC” hereinafter), hard discs and printers have been used most widely. Such a peripheral equipment has been connected to the PC via a multi-purpose digital interface such as an exclusive I/O interface or an SCSI (small computer system interface).
On the other hand, recently, AV (Audio/Visual) equipments such as digital cameras, digital video cameras or the like have also been noticed as one of the peripheral equipment for the PC. Such an AV (Audio/Visual) equipment has also been connected to the PC via an exclusive interface.
However, in the conventional communication system, the digital interface of the peripheral equipment and the digital interface of the AV equipment have no interchangeability, so that these digital interfaces could not interconnected directly. Thus, for example, when a still image is desired to be communicated, the data had to be passed through the PC without fail.
Further, in the conventional exclusive interface and/or SCSI interface, particularly when large capacity data such as a moving image or a still image of the AV equipment is processed, there arose various problems that a data transfer rate becomes low, that a fat communication cable is required for parallel communication, that the number and kind of peripheral equipments capable of being connected are limited, that a connection system is limited and that real time data transfer cannot be effected.
As one of next generation high speed and high performance digital interfaces for solving the above problems, IEEE (The Institute of Electrical and Electronics Engineers, Inc.) 1394-1995 Standard is already known.
The digital interface based upon the IEEE 1394-1995 Standard (referred to as “1394 interface” hereinafter) has the following features:
(1) A data transfer speed is fast.
(2) A real time data transfer system (i.e., isochronous transfer system) and an asynchronous transfer system can be supported.
(3) A connection construction (topology) having high degree of freedom can be fabricated.
(4) A plug-and-play function and a hot-line insertion/withdrawal function are supported.
However, in the IEEE 1394-1995 Standard, although physical and electrical constructions of connectors and two fundamental data transfer systems are defined, there was no definition regarding how to transmit and receive what kind of data through what kind of data format on the basis of what kind of communication protocol.
Further, in the isochronous transfer system based upon the IEEE 1394-1995 Standard, since response to outgoing packets is not stipulated, it is not ensured whether each isochronous packet is positively received. Accordingly, when it is desired that continuous plural data are positively transferred or when it is desired that one file data is positively transferred while dividing it into plural data, the isochronous transfer system could not be used.
Furthermore, in the isochronous transfer system based upon the IEEE 1394-1995 Standard, even when there is vacancy in transfer band, the total number of transmissions is limited to sixty-four. Thus, when it is desired that many transmissions are effected with smaller transfer bands, the isochronous transfer system could not be used.
In addition, in the IEEE 1394-1995 Standard, if bus reset is generated in response to ON/OFF of a power source for nodes or connection/disconnection of the node, data transfer must be interrupted. However, in the IEEE 1394-1995 Standard, if the data transfer is interrupted due to the bus reset or error in transmission, it could not be known what kind of data contents are lost. Further, in order to restore the interrupted transfer, very complicated transmission sequence was required. Incidentally, the bus reset refers to a function for automatically effecting recognition of new topology and the setting of address (node ID) assigned to each node. In the IEEE 1394-1995 Standard, this function can provide the plug-and-play function and the hot-line insertion/withdrawal function.
Further, in the communication system based upon the IEEE 1394-1995 Standard, communication protocol in which (although real time ability is not required) object data (for example, still image, graphic data, text data, file data, program data and the like) having relatively large data amount and requiring reliability are continuously transferred while dividing such data into one or more segment data was not proposed concretely.
Particularly, in the communication system based upon the IEEE 1394-1995 Standard, communication protocol in which data transmission between plural equipments is achieved by using a communication system for broadcasting data in an asynchronous transferring was not also proposed concretely.
Further, when a plurality of such protocols are proposed, it is desirable that a recipient protocol is automatically discriminated and is used properly. However, a method in which a plurality of different communication protocols are used properly was not also proposed concretely.